I did a quick and dirty search about radiators on here and didn't come up with anything, so I figure I'd start this one. The stock radiators now are approaching if not exceeding 20 years of duty (unless replaced). It would be wise to replace them with something that doesn't have a plastic top and bottom. For this cause I've started a list of possible replacements that can be installed with minimal effort into the stock location on the FC.

For starters let’s look at the actual size of the stock radiator (S4): I measured an over all length of 22.5 in and an overall height of 20.25 in. This is of course just a rough estimate because I didn't think it necessary to remove parts of the intake to get an accurate measurement (as even the universal radiators have specific dimensions). The overall thickness of the radiator is about 2.25 in. This includes the end tanks but not the brackets.

The overall length of the core is 21.5 in while the height of the core is roughly 17 in. The estimated thickness of the core is about 1.5 in (may actually be larger, but measurement was just eyeballed to give me an idea).

As for the number of passes or flow type of stock I believe (correct me if I'm wrong anyone) is a single pass. This means the coolant is just dumped into the radiator and at some point works itself down to the lower portion of the radiator as it cools. This is one of the least efficient means of cooling for a few reasons:

The movement of the coolant is not controlled resulting in higher average temperatures across the radiator

The coolant increases in temperature much more rapidly than other flow designs.

Coolant does not have adequate time to cool to a lower temperature. Thus resulting in a higher engine temperature.

With these things in mind we can now look at a few different options. Lets first look at the specifically engineered OE replacements.

Direct OEM Replacements

KOYO

Koyo produces three different radiators for the FC. All are aluminum construction and are a direct fit for the year they are produced. Koyo produces one (1) radiator for the early FC (1986-1988) and two (2) radiators for the late model FC (1989-1991). The main differences are as follows:

The radiator produced for the early FC is (as far as I can tell) a single pass radiator. So although you have an increase in cooling efficiency, you still have the down fall of it being a single pass. Koyo claims a reduction in stock cooling temperatures of about 20-30%. This may be an affordable option for those who have not heavily modified their cars and are just looking for a slight increase in cooling performance. This is a direct replacement with OEM (just remember to keep the brackets to mount the radiator).

The second radiator produced by Koyo for the FC is for the S5. Similar to the previous radiator discussed it too is a single pass radiator style. On the other hand, the final radiator produced by Koyo for the S5 is an "N-Pass" flow pattern which increases the ability of the radiator to cool the engine significantly. The "N-pass" is basically a 3 pass flow pattern allowing the coolant to remain in the radiator and cool to a lower temperature before returning to the engine. This radiator comes highly recommended by those who have installed it. But may be overkill depending on your level of modification.

All the Koyo radiators retail for anywhere between 300-400 dollars.

CorkSport

Along these same lines Corksport produces their own similar radiator for the FC (both S4 and S5) at a slightly lower cost. The radiator is single pass aluminum construction. Which leads me to assume a similar efficiency to that of the single pass Koyo's (about 20-30%). Expect to pay around 300 plus shipping for one.

Fluidyne

Fluidyne offers similar radiators for the FC as the Koyo, however they are slightly more expensive--starting at 400 and only increasing from there depending on where you order yours from. Effeciency is similar to the Corksport and Koyo.

AWR/Ron Davis

AWR/Ron Davis offer two different radiators for the FC. One being a single pass and one being a Dual-Pass cross flow. These radiators are usually built for racing and as such their price reflect that. I can not find the stats on the single pass beyond the fact that there are no pre-drilled mounting holes on the mounting tab to allow you to mount the radiator specifically where you'd like it to be. Looking at the radiator it seems to me to be a down flow design, however I may be mistaken on that.

There is also the AWR/Ron Davis cross flow radiator. It is signifcantly more effecient than the Single pass radiators and offers increased cooling benefits as the coolant has to travel accross the radiator multiple times before being returned to the engine (I believe it's a cross flow two pass radiator). Construction is also different than the radiators mentioned above. The core is fully tig welded while the ones above are brazed. However with all these benefits they carry a hefty price tag. Ranging from mid 400 to upper 500 depending on where you purchase them. The dimensions of that radiator are as follows:with an overall length of 28 in and a height of 19 in. The core is 18.25 in. in height and 24 in. in length while the core is 2.25 in. thick.

CSF

CSF offers a few different radiators for each individual year. For S4 they sell radiator No. 864. It is an all metal replacement for the OE radiator. Beyond the same dimensions as stock with metal end tanks little else is declared from their site (no price tag either). Dimensions:
Core Size 16-3/4 x 22-1/8 x 1-5/16
Tank Size Inlet 22-1/6 x 1-9/16
Outlet 22-1/6 x 1-9/16
Hose Fittings Top 1-1/2 Right
Bottom 1-1/2 Right
No of Rows 2

CSF also offers another radiator for S5's but with the same stock dimensions. Radiator No. 2006. Dimensions are as follows:

Universal type radiators... what can I say about these? They are remarkably cheaper for the amount of radiator you get. This isn't necessarily reflected in the workmanship of the product but the cost savings come to you by the ability of the company to mass produce the radiator to specific dimensions and sell to a wider range of applications. Since there are so many universal radiators available it would be impossible for me to list them all and keep them all updated. For this cause I will list a few radiators from different companies. Note that depending on your situation you may need to either alter the universal radiator, pick a smaller one, or even modify the radiator supports to accept the sizes I recommend.

Keep in mind that no matter what radiator you decide to go with you need to be aware of how much heat your engine is generating. Do not select a small or medium 4-pass 3-core Cross flow radiator and expect tremendous cooling capacity to cool your insanely large turbo and heavily ported engine. It just doesn't work like that. You will always get more cooling capacity from more surface area. Period. The larger the radiator the better (there is a point of diminishing returns, but just as a rule of thumb that will work). My personal recommendations is a two or three core radiator should be standard (for the most part, they are. It's quite difficult to find a single core radiator, and why would you even want one? I don't know). Single pass will be fine for stock to slightly modified and any pass (2,3, 4, x pass) will be fine for slightly modified to extremely modified. This is of course, a rule of thumb and you will need to figure out your own cooling needs before putting on any radiator. Alright, enough. On with it already:

AFCO

I believe Ted said it best: These radiators offer the same level of cooling as Ron Davis but at a fraction of the cost

Quote:

Originally Posted by Ted

[A]n AFCO Racing 80125N is about the same thing...for under $300.

The only catch is that keeping the stock battery (tray) is next to impossible. It's a 26" width rad, so things get tight up front, but it does fit between the engine frame rails; [t]here are several options to mount this unit, but be prepared to do some minor cutting.

Some specs...
The rad has the hose fittings on the proper sides...The top hose is 1.5" - same as stock. The bottom hose is 1.75" - stock is 1.5"; we use auto parts stores generic hose that's around 11" long but uses a 1.5" on one side and 1.75" on the other - perfect. It is a double-pass design for better efficiency. It's a 3" thick core. It uses a "domestic" type rad cap on the rad - need to buy separately. The rad cap filler neck does have a 1/8" NPT fittings for bypass use. This filler neck makes it easy to bleed air out of the system. If you want to add any of the stock FC stuff - lower thermoswitch, coolant level, heater hose - you need to add / fab them yourself.

Which brings up a very good point. Many of the universal radiators do not have the appropriate holes or bungs for the different sensors. Be aware that if you wish to retain those sensors you'll need to drill, tap, and/or weld in the appropriate fittings to mount the sensor. One may also need to modify the mounting location to make sure there's enough space and a proper alignment for good airflow.

**Note: This portion is still under going modification**
Here's a brief explination of the different radiator types:Single Pass:
This picture isn't 100% accurate. It does give a general idea of how the temperature is going to look across the radiator though. Since hotter fluid is less dense than colder fluid the heat is spread more evenly across the top (since stock is down flow instead of cross). This results in the hotter portion of the coolant being retained above the cooler portion before it is all returned to the engine via the lower outlet. This however is not all that effecient from a cooling standpoint as the radiator begins to heatsoak. The hotter coolant will eventually raise the average temperature throughout the radiator causing the radiator to return hotter and hotter coolant. However--this is completely dependent on your heat generating modifications (turbo, etc).Double Pass:The double pass is slightly more effecient at cooling. This is a cross flow type where the hot incoming coolant is cooled as it travels accross the radiator. It is then further cooled when it travels accross the radiator again to the outlet. This kind of setup is helpful in that the coolant is given far more time to cool as it travels accross the radiator. Unfortunatly this also reduces turbulence with the coolant and therefore reduces heat transfer capacity. If turbulence can be added the coolant will transfer more heat more effectively... but that's a discussion for another section.Triple Pass:
*Picture Forth Coming*
A triple pass or an N-Pass is similar to the 2 pass radiator in that it allows the coolant more time to cool. Again, the coolant is passed from one section of the radiator to another, and at each time it is exposed to more (cooler, and cooler) surface temperatures before being returned to the engine block.4-Pass:
The biggest pass I've ever heard about. Usually reserved for large displacement and heavy horsepower applications a 4-pass radiator starts to see a diminishing return in cooling ability. These radiators are rare to come by in off the shelf type, and usually are reserved for custom manufacture (Read that as expensive). The idea is taking a 2-pass and basically adding another 2-pass below it. You get twice the cooling time as a regular 2-pass, but you have to make a compromise. That is either in weight, or in the amount of coolant that is being pulled into the engine. If the volume of coolant available to the engine remains the same (effectively doubling surface area), you make up for the cooling performance in weight. If teh volume of coolant is allowed to decrease to maintain specific surface area of the radiator,then the effective time for the coolant to cool is reduced as it pushes more coolant to the engine sooner. The best adivce with regard to these radiators would be: know your goals and understand that a 4-pass may be overkill for a majority of the cars out there.

Number Of Rows (Cores)

Single Row
The number of rows is a balancing act between the cooling ability of the radiator and the weight to which you wish to hold your car. Usually single row radiators are used strictly in racing in which air flow is always occuring over the radiator providing enough CFM to allow the heat to dissappate quickly with little repercussions on the engine. On the road, might not be the best option as we deal with stop and go traffic and the heat may not dissappate quickly enough to maintain a healthy engine.

Double Row
Double rows are fairly common, especially on stock radiators. These handle a fair amount of heat and are able to hold more coolant in a double row compared to a single row. This however has drawback that as the radiator reaches temperature, the radiation from the front row will pass on to the rear. But this radiation is usually neglible at speed.

Triple Row
Triple rows improve upon the cooling ability of the radiator another step. Similar to the Double Row it maintains the same pros and cons. The added benefit of the multi-row radiators is that they allow for additional coolant to be available to the engine. This decreases the chances of over heating yet raises the average temperature gradient over the radiators surface area.

I like FerociousP's set up. It is a THICK radiator meant for some GM (we think). It sits perfectly upright in the stock location (no angle like stock), and the Escort fan fits on it perfect as well. The thing is beefy!!

Thanks for pointing out that company. I'll be covering universals next (I can't seem to find anymore specific companies that built specific OEM replacement rads)

Quote:

Originally Posted by J-Rat

I have a K2RD radiator which is no longer made that is a Dual Pass. I do have all the drawings and part numbers to make them again.

Are you planning on making some more? out of curiousity, how is the cooling with the Dual Pass compared to a single pass? I'm looking for some real world reactions and experiences when it comes to radiators. What works, what doesn't, etc.

Thanks for pointing out that company. I'll be covering universals next (I can't seem to find anymore specific companies that built specific OEM replacement rads)

Are you planning on making some more? out of curiousity, how is the cooling with the Dual Pass compared to a single pass? I'm looking for some real world reactions and experiences when it comes to radiators. What works, what doesn't, etc.

Well, I actually think Ted was involved in making them the first time. They are AFCO cores made with custom end-tanks to fit OEM mounting positions. As far as making them again, I need to make sure the originating company doesnt have any problems with that.

CSF radiators are also good and inexpensive. I have a 2-row that costed me a little more than 200 bucks shipped brand new. On a 99 degree trackday, my temps stayed at 100C during 25 minute sessions, and reached an occasional high of 105C. Normal driving temps were about 82-88C

CSF radiators are also good and inexpensive. I have a 2-row that costed me a little more than 200 bucks shipped brand new. On a 99 degree trackday, my temps stayed at 100C during 25 minute sessions, and reached an occasional high of 105C. Normal driving temps were about 82-88C

If the Ron Davis units require that kinda fabrication to install, then an AFCO Racing 80125N is about the same thing...for under $300.
The only catch is that keeping the stock battery (tray) is next to impossible.
It's a 26" width rad, so things get tight up front, but it does fit between the engine frame rails.
There are several options to mount this unit, but be prepared to do some minor cutting.
These are really for "race" cars with extensive mods, or owners are prepared to do mods for function over form.
I tend to lop off most of the original radiator brakets on the car for this install.
I'm close to completing my FMIC install, so I'll try and post pics of my install with this rad soon (don't hold your breath now).

We've tested this unit on our race car up at Thunderhill in the middle of summer in 100F+ ambients.
It was able to keep the coolants temps under 205F no problem.

Some specs...
The rad has the hose fittings on the proper sides - none of this Chevy / Ford crossover hose crap.
The top hose is 1.5" - same as stock.
The bottom hose is 1.75" - stock is 1.5"; we use auto parts stores generic hose that's around 11" long but uses a 1.5" on one side and 1.75" on the other - perfect.
It is a double-pass design for better efficiency.
It's a 3" thick core.
It uses a "domestic" type rad cap on the rad - need to buy separately.
The rad cap filler neck does have a 1/8" NPT fittings for bypass use.
This filler neck makes it easy to bleed air out of the system.
If you want to add any of the stock FC stuffs - lower thermoswitch, coolant level, heater hose - you need to add / fab them yourself.

I like FerociousP's set up. It is a THICK radiator meant for some GM (we think). It sits perfectly upright in the stock location (no angle like stock), and the Escort fan fits on it perfect as well. The thing is beefy!!

Well... I found out the maximum post length... so continuing post number 1 here now.

Universal Radiators Continued...

Of consequence there are occasions when electrolosis does occur on an aluminum radiator. To counter this problem one should make sure that the radiator is properly installed with rubber bushings. Also, find the route cause of the problem (your electrical system) and rectify it. That being said a properly setup radiator should have no electrolosis occuring within it, let alone any electrical current or voltage gounding it out--this means it is isolated from the chasis using non-conductive material such as rubber bushings (but then again, maybe I'm just being anal ).

Griffen Universal Radiators
One of the only radiators that Griffen offers within the stock dimensions is the Griffin 2-28185-X. It is a Scirocco style which means it has both the inlet (1.5 in) and outlet (1.75 in) on the same side (passenger or driver if you flip it up side down). It is 22 in x 13 in x 3 in overall. It is a dual-row two pass radiator and has a price tag of about 275 at summitracing.

If you have any questions or comments post up. It'll help make this thread better.

Okay people, I'm going to need your help from here on out. I would like real world numbers from people. Those running stock radiators I would like you to voice your opinions concerning them. Vitally important details I would really like to see would be Ambient Air temperatures, Water temperatures at idle (nominal), water temperatures at cruise and if possible under load as well.

For those who have already swapped over to an aluminum radiator I would like similiar information.
Ambient air temperatures.
Coolant Temperatures at Idle.
Coolant Temperatures under load and/or cruise.
Also I would like to know how much body modification you had to do to mount the radiators, and if how much time you spent doing so.